1. Field of the Invention
The present invention relates generally to apparatus for molding by inoculation of cast iron parts requiring a spheridal graphite texture, and more particularly to apparatus for molding or casting rather large parts, such as for example, the crankshafts of internal combustion engines.
2. Description of the Prior Art
Inoculation of molten iron for the purpose of improving the texture of the cast components, with the aid of additional alloys, such as for example, silicon and magnesium and various metals, and especially for obtaining a spheroidal graphite texture, is of course known. It is also a known fact that the effect of the inoculation decreases rapidly with time whereby it is most desirable to perform such process immediately before the solidification of the metal so treated if a homogeneous structure is to be obtained.
Many inoculation techniques and apparatus for carrying out the same have been employed for this purpose, such as for example, one such technique wherein the finely divided inoculant has been introduced into the melt prior to pouring, the inoculant and melt being mixed together within the ladle. Another technique of double inoculation has also been utilized, the melt being initially inoculated within the ladle prior to the commencement of the pouring operation and the inoculation being subsequently repeated immediately prior to pouring either, for example, during the course of transferring the composition within small hand ladles, or by passage through funnel-configured filters containing a suitable quantity of the inoculant. An attempt has also been made to inoculate the molten metal by a continuous process or repeated, directly applied dispersions within the gate, or by means of the introduction of powdered inoculent into the mold.
These techniques however, have not been proven sufficiently reliable with respect to the homogeneity of the texture of the castings, and consequently apparatus was conceived whereby the molten iron would be placed in contact with the inoculant while the same was flowing within the system of channels or runners of the mold, the inoculant coating or forming a body fixedly held within the mold and preferably being in the form of a perforated mold core which would be able to be progressively dissolved by means of the molten metal pouring in around it.
Within a more sophisticated version of the preceding apparatus, the fragmented inoculant would be placed within the runners of the mold immediately upstream of an arrangement, such as for example, a grill of refractory material or a perforated mold core which thereby permits passage therethrough of the molten metal and dissolved inoculant while intercepting and retaining undissolved inoculant particles.
Within these apparatus facilitating progressive dissolution of the inoculant particles by means of the poured metal, it is necessary however that the dimensions of the particles, when the pouring operation is finished, be greater than those of the openings within the grill so as to allow only the passage therethrough of the molten metal and dissolved inoculant. As a result, greater quantities of inoculant than required for achieving a particular texture, must be used and the residual inoculant embedded within the deadhead subsequent to solidification is lost. In addition, if undissolved particles of inoculant, having dimensions smaller than that of the grill, pass therethrough, the texture of the resulting composition will obviously be deleteriously affected.
Furthermore, during the time between the start and finish of the pouring operation, there is great variation within the exchange surface between the molten metal and the inoculant, causing in particular a decrease in the degree of inoculation. If this is not too objectionable for the casting of small pieces, such is to the contrary for rather massive parts, such as for example, the crankshafts of internal combustion engines which require a rather long time for the pouring operation, there thus being a great risk of insufficient homogeneity within the texture thereof.